A mobile communication device includes a receiving circuit having a low-noise amplifier (LNA) so that good receiving characteristics can be obtained even when a received signal is weak. In this LNA, a bypass switch is sometimes provided so as to change the signal gain. In general, the bypass switch is connected in parallel with an amplifier part of the LNA and thus provides a bypass route between input and output terminals of the amplifier part.
However, since the input impedance of the field-effect transistor (FET) used for the amplification in the LNA is typically very high, the input impedance of the receiving circuit increases when the bypass switch is off. On the other hand, when the bypass switch is turned on, the bypass switch connects between input and output terminals, whereby the input impedance of the receiving circuit decreases. Therefore, depending on the state of the bypass switch, a large difference can be caused in the input impedance of the receiving circuit. In such a case, the input impedance of the receiving circuit might not be appropriately matched to the characteristic impedance of the system including the receiving circuit. As a result, good receiving characteristics cannot be obtained with this receiving circuit.